From the prior art it is known to connect, downstream from main transmissions in the power flow of a powertrain, transmission devices or longitudinal transfer transmissions which serve to distribute the torque delivered by at least one drive motor of the vehicle to at least two driven vehicle axles in the longitudinal direction of a vehicle.
In addition it is known to distribute the drive torque delivered to a driven vehicle axle between the two drive wheels of the vehicle axle, whereby the drive wheels of a driven vehicle axle can be driven at different speeds independently of one another in accordance with the different path lengths of the left and right tracks; in this way the drive torque can be distributed to the two drive wheels without producing any yawing moment.
In this situation, due to the compensating action of a differential transmission, the propulsion forces of the two drive wheels of one or more driven vehicle axles that can be transmitted to the road are governed in each case by the lower or lowest drive torque of the two drive wheels or driven axles that can be transmitted, and this has the disadvantageous result that if a drive wheel, for example one that is on glazed frost, undergoes wheel-spin, the torque delivered to the other drive wheel, the one on a gripping surface, cannot be any greater than that delivered to the spinning drive wheel. Accordingly, in such a situation, due to the compensating action of a differential transmission which enables a speed difference to exist between the two output shafts of the differential transmission, the vehicle cannot start moving.
To avoid this, in the prior art it has been proposed that in the event of critical driving conditions the compensating action of differential transmissions should be prevented by appropriate measures, for example by blocking the differential transmission by means of a differential lock.
DE 103 48 959 A1 by the present applicant describes a transmission device for distributing drive torque to at least two output shafts, which comprises at least two planetary gearsets each with at least three shafts, such that in each case a first shaft of a planetary gearset is connected to a drive input shaft and in each case a second shaft of a planetary gearset is one of the output shafts. In this known transmission device it is provided that in each case a third shaft of the planetary gearsets is in active connection with a brake in such manner that a degree of distribution of the drive torque between the two output shafts varies as a function of the transmission capacity of the brakes.
By virtue of the transmission device known from DE 103 48 959 A1 a transmission device should be provided, which is of simple design, inexpensive to produce, and by means of which a degree of drive torque distribution between two output shafts can be varied according to need.
According to DE 103 48 959 A1 it is provided that the third shaft of the planetary gearsets are functionally connected to one another, this functional connection being realized in each case by a brake by means of which, with a correspondingly set transmission capacity, in each case a torque can be supported by a housing of the transmission device and such that the two brakes can be controlled by a separate control unit or by the transmission control unit of the transmission device.
Here, the functional connection of the respective third shaft of the planetary gearsets with one another consists of two mutually parallel power paths, the first power path comprising a third planetary gearset that can be connected into the force flow of the transmission by means of a claw clutch and the second power path consisting of the transmission housing and the two brakes, which are respectively connected to the sun gear of the first planetary gearset and the sun gear of the second planetary gearset, such that in the engaged condition the two sun gears of the planetary gearsets are fixed relative to the housing. When the two brakes are engaged at the same time, the compensating action of the transmission is completely blocked so that the two output shafts rotate at the same speed.
When the claw clutch associated with the third planetary gearset is disengaged, by suitably controlling the two brakes a distribution degree of the drive torque between the two output shafts ranging between 0% and 100% can be achieved, such that to reduce power losses it is preferable for one respective brake to be in the engaged condition while the respective other brake is operated between a fully disengaged condition and a fully engaged condition.
When the brakes are disengaged and at the same time the claw clutch is engaged, the drive torque delivered to the transmission is distributed as a function of a basic distribution of the transmission to the two output shafts, this basic degree of distribution being determined by the ratio of the number of teeth on the ring gear to the number of teeth on the sun gear of the third planetary gearset. As a function of a braking torque applied by one of the brakes, the basic degree of distribution can be changed in a continuously variable manner in the direction of an upper or a lower limit value of the degree of distribution.
Thus, the known axle or distributor transmission can be operated in two modes, such that in the first mode with the claw clutch disengaged, the drive torque is distributed between the two output shafts, whereas in the second mode, with the claw clutch engaged, the effect of a spur gear differential is produced between the two outputs.
Disadvantageously, to operate the transmission device known from DE 103 48 959 A1 a total of three actuating devices are needed, a respective actuating device being associated with each of the two brakes and with the claw clutch. Furthermore, in the differential mode, i.e. with the claw clutch engaged, drag torques are disadvantageously produced by the disengaged brakes.